increasing the ethernet MTU greater than 1500 (1502)

kamal kc kamal_ckk at
Thu Jan 5 23:18:08 PST 2006

dear everbody,

i have working to compress/decompress the packets. 
i know there are various schemes and facilities to 
do so in the freebsd, i have developed the 
compression facility myself.

i am just a beginner in freebsd programming and
in network programming.

since i compress packet i add 2 byte custom header. 
now the problem is when the MTU sized packet is 
incompressible, i still add my 2 bytes which exceeds 
the MTU (1500) and the size becomes 1502. 

there was two options for me :
either fragment the packet or increase the mtu.

i don't want to fragment the packet as i think 
that is too much overhead for 2 bytes. rather i 
want to increase the mtu. 

i tried 
-->ifconfig xl1 mtu 1502

but it gave the message:
-->ifconfig: ioctl (set mtu): invalid argument

How can i increase the MTU ??? 
Will it have any effect whatsoever ???
i guess ethernet should support MTU of 1502. isn't it
correct ??

help !!


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